The invention relates to metal-clad polymer articles comprising amorphous or fine-grained metallic coatings/layers on polymeric-composite materials/substrates with good adhesion and thermal cycling performance for use in structural applications.
Due to their low cost and ease of processing/shaping by various means, polymeric materials, which are optionally filled with, or reinforced with, materials selected from the group of metals, metal alloys, and/or carbon based materials selected from the group of graphite, graphite fibers, carbon, carbon fibers and carbon nanotubes, glass, glass fibers and other inorganic fillers, are widely used.
Applying metallic coatings or layers to the surfaces of polymer parts or vice versa is of considerable commercial importance because of the desirable properties obtained by combining polymers and metals. Metallic materials, layers and/or coatings are strong, hard, tough and aesthetic and can be applied to polymer substrates by various low temperature commercial process methods including electroless deposition techniques and/or electrodeposition. The metal deposits must adhere well to the underlying polymer substrate even in corrosive environments and when subjected to thermal cycling and loads, as encountered in outdoor or industrial service.
The prior art describes numerous processes for metalizing polymers to render them suitable for metal deposition by conditioning the substrate's surface to ensure metal deposits adequately bond thereto resulting in durable and adherent metal coatings. The most popular substrate conditioning/activation process is chemical etching.
Stevenson in U.S. Pat. No. 4,552,626 (1985) describes a process for metal plating filled thermoplastic resins such as Nylon-6®. The filled resin surface to be plated is cleaned and rendered hydrophilic and preferably deglazed by a suitable solvent or acid. At least a portion of the filler in the surface is removed, preferably by a suitable acid. Thereafter electroless plating is applied to provide an electrically conductive metal deposit followed by applying at least one metallic layer by electroplating to provide a desired wear resistant and/or decorative metallic surface. Stevensen provides no information on thermal cycling performance or adhesion strength.
Leech in U.S. Pat. No. 4,054,693 (1977) discloses processes for the activation of resinous materials with a composition comprising water, permanganate ion and manganate ion at a pH in the range of 11 to 13 exhibiting superior peel strengths following electroless metal deposition. Leech provides no information on thermal cycling performance, and adhesion strength is exclusively measured using a peel test.
Nishizawa in U.S. Pat. No. 5,185,185 (1993) discloses methods for pretreating polymeric resin molded articles molded from various resins and a glass-reinforcing agent such as glass fibers by (i) treating the resin molded article by immersion in an oxidative acid solution, (ii) treating the resulting resin molded article by immersion in an organic polar solvent-containing liquid, and (iii) treating the resulting resin molded article by immersion in a solvent which can dissolve one or both of the glass reinforcing agent and one or more of the other thermoplastic resins. The use of ammonium fluoride as glass fiber etchant is shown to enhance adhesion. Nishizawa provides no information on thermal cycling performance and reports peel strength data ≦1.5 kg/cm (≦14.7 N/cm).
Yates in U.S. Pat. No. 5,863,410 (1999) describes an electrolytic process for producing copper foil having a matte surface with micropeaks with a height not greater than about 200 microinches (˜5 micron) exhibiting a high peel strength when bonded to a polymeric substrate.
Various patents address the fabrication of articles for a variety of applications:
Watanabe in U.S. Pat. No. 6,996,425 (2006) describes a cellular telephone housing formed from a polymeric material by molding, wherein the base is coated with a metal multi layer to about 10 micron thickness, including a lower metal layer (adjacent to the polymer substrate) made of a ductile metal such as Cu and an upper metal layer made of a less ductile metal such as Ni to achieve high strength, rigidity and shock resistance. The ductile metal layer is 4-5 times thicker than the upper metal layer. Watanabe provides no information on thermal cycling performance or adhesion strength.
Erb in U.S. Pat. No. 5,352,266 (1994), and U.S. Pat. No. 5,433,797 (1995), assigned to the same applicant, describe a process for producing nanocrystalline materials, particularly nanocrystalline nickel based materials. The nanocrystalline material is electrodeposited onto the cathode in an aqueous electrolyte by the application of a pulsed current.
Palumbo in US 2005/0205425 A1 (2002) and DE 10,228,323 (2005), assigned to the same applicant, discloses a process for forming coatings or freestanding deposits of nanocrystalline metals, metal alloys or metal matrix composites. The process employs tank plating, drum plating or selective plating processes using aqueous electrolytes and optionally a non-stationary anode or cathode. Nanocrystalline metal matrix composites are disclosed as well.
Tomantschger in US 2009/0159451 A1, assigned to the same applicant, discloses variable property deposits of fine-grained and amorphous metallic materials, optionally containing solid particulates.
Palumbo in U.S. Pat. No. 7,320,832 (2008), assigned to the same applicant, discloses means for matching the coefficient of thermal expansion (CTE) of fine-grained metallic coating to the one of the substrate by adjusting the composition of the alloy and/or by varying the chemistry and volume fraction of particulates embedded in the coating. The fine-grained metallic coatings are particularly suited for strong and lightweight articles, precision molds, sporting goods, automotive parts and components exposed to thermal cycling and include selected polymeric substrates. Maintaining low CTEs (<25×10−6 K−1) and matching the CTEs of the fine-grained metallic coating with the CTEs of the substrate minimizes dimensional changes during thermal cycling and preventing delamination. Palumbo provides no information on the adhesion strength.
Palumbo in U.S. Pat. No. 7,354,354 (2008), assigned to the same applicant, discloses lightweight articles comprising a polymeric material at least partially coated with a fine-grained metallic material. The fine-grained metallic material has an average grain size of 2 nm to 5,000 nm, a thickness between 25 micron and 5 cm, and a hardness between 200 VHN and 3,000 VHN. The lightweight articles are strong and ductile and exhibit high coefficients of restitution and a high stiffness and are particularly suitable for a variety of applications including aerospace and automotive parts, sporting goods, and the like. Palumbo provides no information on thermal cycling performance or adhesion strength. To enhance the adhesion of the metallic coating the surface to be coated is roughened by any number of suitable means including, e.g., mechanical abrasion, plasma and chemical etching.
Andri in WO 2009/045431 describes portable electronic devices comprising a structural synthetic resin and structural coatings of fine-grained metallic materials for added strength, rigidity and impact resistance. According to Andri the metal adheres well to the synthetic resin without any special treatment; however, a method for improving adhesion can be used including abrasion, addition of adhesion promotion agents, chemical etching, functionalization of the surface by exposure to plasma and/or radiation or any combination of these. Andri provides no information on thermal cycling performance or adhesion strength.
Andri in WO 2009/073435 describes automotive parts with a composition comprising partially aromatic polyamide (PAP), aliphatic polyamide and/or polymeric toughener and alkaline earth metal carbonate e.g. calcium carbonate. The polymer is activated using mechanical and/or chemical etching, specifically acidic materials such as sulfochromic acid, hydrochloric acid or sulfuric acid.